Media transport system turnover mechanism

ABSTRACT

A media turnover mechanism includes a roller. A first turn bar is positioned upstream relative to the roller at an angle relative to a direction of media motion. A second turn bar is positioned downstream relative to the roller at an angle relative to a direction of media motion. A first guide is positioned between the first turn bar and the roller to direct a leading edge of a web of media toward the roller. A second guide is positioned between the roller and the second turn bar to direct the leading edge of the web of media toward the second turn bar. A third guide is positioned to direct the leading edge of the web of media around the second turn bar.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned copending U.S. patent application Ser. No. 12/627,032 filed Nov. 30, 2009 entitled “MODULAR MEDIA TRANSPORT SYSTEM”, by DeCook et al., commonly-assigned copending U.S. patent application Ser. No. 12/627,018 filed Nov. 30, 2009 entitled “MEDIA TRANSPORT SYSTEM FOR NON-CONTACTING PRINTING”, by Muir et al., and Ser. No. ______ (Docket 96218), entitled “MEDIA TRANSPORT SYSTEM DRIVE MODULE”, by Armbruster et al. filed concurrently herewith.

FIELD OF THE INVENTION

The present invention generally relates to a media transport system and more particularly relates to a mechanism for flipping the media while in motion in order to switch the relative orientation of top and bottom surfaces of the moving web media within the media transport system.

BACKGROUND OF THE INVENTION

Continuous web printing allows economical, high-speed, high-volume print reproduction. In this type of printing, a continuous web of paper or other substrate material is fed past one or more printing subsystems that form images by applying one or more colorants onto the substrate surface. Performance criteria for mechanical apparatus that handle paper or other print media traveling at high speeds throughout the printing process include efficiency and speed as well as the capability to maintain precise registration.

In a number of systems of this type, both surfaces of the web media are printed on. After the first side of the media has been printed upon, the media transport system flips the print media over while in motion, in order to print onto the other surface of the web. Subsystems that perform this function have been called turnover apparatus, turnbar apparatus, or “turnover modules”, for example, and typically consist of an arrangement of fixed or moving rollers that direct and re-orient the moving web accordingly.

One difficulty with conventional turnover apparatus relates to initial feed of the print media by an operator when loading the machine for a print job. Turnover apparatus often direct the media over a somewhat complex feed and guidance path, changing path direction a number of times in order to perform the flipping function. This path typically extends around and between a number of rollers and fixed surfaces that are positioned at different angles and, because the turnover mechanism is often difficult to see and to access in the first place, it can be a cumbersome operation often requiring two people to accomplish. Time and training requirements for this operator function can be burdensome.

The capability to feed the leading edge of a print media roll through the media transport path quickly and accurately can translate to increased efficiency, reduced cost, and reduced likelihood of jams, dirt, and other problems for continuous web printing. Thus, there is a need for an improved leading edge guidance solution for high-speed, non-contact, continuous web printers.

SUMMARY OF THE INVENTION

It is an object of the present invention to advance the art of web media handling. With this object in mind, the present invention provides solutions for improving leading edge guidance through a continuous web media transport system and, in particular, through the media turnover mechanism of such a transport system.

According to one feature of the present invention, a media transport system turnover mechanism includes a number of guides for directing the leading edge of the media through the turnover mechanism.

According to another feature of the present invention, a media turnover mechanism includes a roller. A first turn bar is positioned upstream relative to the roller at an angle relative to a direction of media motion. A second turn bar is positioned downstream relative to the roller at an angle relative to a direction of media motion. A first guide is positioned between the first turn bar and the roller to direct a leading edge of a web of media toward the roller. A second guide is positioned between the roller and the second turn bar to direct the leading edge of the web of media toward the second turn bar. A third guide is positioned to direct the leading edge of the web of media around the second turn bar.

One advantage of the present invention is that it provides a measure of guidance for routing a media web along a travel path, around and between rollers, surfaces, and other components of the printing system. Another advantage of the present invention is that it provides media web guidance without adding constraint to media edges.

The invention and its objects and advantages will become more apparent in the detailed description of the example embodiments presented below. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:

FIG. 1 is a schematic side view of a digital printing system according to an example embodiment of the present invention;

FIG. 2 is an enlarged schematic side view of media transport components of the digital printing system shown in FIG. 1;

FIG. 3 is a top schematic view showing the arrangement of rollers and surfaces in a turnover mechanism shown in FIG. 2;

FIG. 4 is a side view of digital printing system components according to an example embodiment of the invention;

FIG. 5 is a perspective view of a prior art turnover mechanism showing media path directions;

FIG. 6 is a perspective view of the turnover mechanism shown in FIGS. 3 and 4 showing guide positions between turn bars and the fixed drive roller;

FIG. 7 is another perspective view of the turnover mechanism showing guide positions between turn bars and the fixed drive roller;

FIG. 8 is a top view of the turnover mechanism showing guide positions;

FIG. 9 is a partial side view of a turnover mechanism showing components of a media drive module and guides according to an example embodiment of the invention;

FIG. 10 is a plan view of a media guide that fits over a nip roller in the media drive module;

FIG. 11 is a side view of the media drive module showing a media guide in an operating position; and

FIG. 12 is a side view of the media drive module showing the media guide in a loading position.

DETAILED DESCRIPTION OF THE INVENTION

The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.

The method and apparatus of the present invention provide a guidance mechanism to improve leading edge feed of the web media through the set of rollers and drive mechanism of a turnover apparatus in a continuous web media transport apparatus.

The method and apparatus of the present invention provide a turnover apparatus in a digital printing system that transports continuously moving web print media past one or more digital printheads, such as inkjet printheads. The apparatus and method of the present invention are particularly well suited for printing apparatus that provide non-contact application of ink or other colorant onto a continuously moving medium. The printhead of the present invention selectively moistens at least some portion of the media as it courses through the printing system, but without the need to make contact with the print media.

In the context of the present disclosure, the term “continuous web of print media” relates to a print media that is in the form of a continuous strip of media as it passes through the printing system from an entrance to an exit thereof. The continuous web of print media itself serves as the receiving print medium to which one or more printing ink or inks or other coating liquids are applied in non-contact fashion. This is distinguished from various types of “continuous webs” or “belts” that are actually transport system components rather than receiving print media and that are typically used to transport a cut sheet medium in an electrophotographic or other printing system. The terms “upstream” and “downstream” are terms of art referring to relative positions along the transport path of a moving web; points on the web move from upstream to downstream.

Referring to the schematic side view of FIG. 1 and enlarged view of FIG. 2, there is shown a digital printing system 10 for continuous web printing according to a modular embodiment. A first module 20 and a second module 40 are provided for guiding continuous web media that originates from a source roller 12. Following an initial slack loop 52, the media that is fed from source roller 12 is then directed through digital printing system 10, past one or more digital printheads 16 and supporting printing system 10 components. First module 20 has a support structure, shown in more detail subsequently, that includes a cross-track positioning mechanism 22 for positioning the continuously moving web of print media in the cross-track direction, that is, orthogonal to the direction of travel and in the plane of travel. In one embodiment, cross-track positioning mechanism 22 is an edge guide for registering an edge of the moving media. A tensioning mechanism 24, affixed to the support structure of first module 20, includes structure that sets the tension of the print media. Rollers and fixed surfaces A, B, C, D, E, F, G, and H guide the moving media through first module 20.

Downstream from first module 20 along the path of the continuous web media, second module 40 also has a support structure, similar to the support structure for first module 20. Affixed to the support structure of either the first or second module 20 or 40 are one or more angular constraint structures 26, such as rollers, for setting an angular trajectory of the web media. Rollers I, J, K, L, M, N, O, and P guide the moving media through and out from second module 40.

Still referring to FIGS. 1 and 2, printing system 10 also includes a turnover mechanism (TB) 30 that is configured to turn the media over, flipping it backside-up in order to allow printing on the reverse side. The print media then leaves the digital printing system 10 and travels to a media receiving unit, in this case a take-up roll 18. Take-up roll 18 is then formed from the re-wound printed web media. The digital printing system can include a number of other components, including multiple print heads and dryers, for example, as described in more detail subsequently. Other examples of system components not described herein but common to such systems include web cleaners, web tension sensors, and quality control sensors.

Control logic for the respective digital printing system 10, shown at control logic processor 90 in the FIG. 2 embodiment, monitors load cell signals at one or more locations and, in response, makes any needed adjustment in motor torque in order to maintain the proper level of tension throughout the system. For the embodiments of FIGS. 1 and 2, the pacing drive component of the printing apparatus is turnover mechanism TB 30. There are two tension-setting mechanisms, one preceding (upstream from) and one following (downstream from) turnover mechanism TB 30. On the input side, load cell signals at roller D (FIG. 2) indicate tension of the web preceding turnover mechanism TB 30; similarly, load cell signals at roller J indicate web tension on the output side, between turnover mechanism TB 30 and take-up roll 18. Control logic for the appropriate in- and out-feed driver rollers at B and N, respectively, can be provided by an external computer or processor, not shown in Figures of this application. Optionally, on-board control logic processor 90, such as a dedicated microprocessor or other logic circuit, can be used for maintaining control of web tension within each tension-setting mechanism and for controlling other machine operation and operator interface functions. As described, the tension in a module preceding turnover mechanism TB 30 and a module following turnover mechanism TB 30 can be independently controlled relative to each other, further enhancing the flexibility of the printing system. In this example embodiment, the drive motor is included in turnover mechanism TB 30. In other example embodiments, the drive motor need not be included in a turnover mechanism. Instead, the drive motor can be appropriately located along the web path so that tension within one module can be independently controlled relative to tension in another module.

Table 1 that follows identifies the lettered components used for web media transport and shown in FIG. 2. An edge guide, against which the media is urged laterally so that an edge of the media contacts a stop, is provided at A. The slack web entering the edge guide allows the print media to be shifted laterally without interference without being overconstrained. An S-wrap device SW provides stationary curved surfaces over which the continuous web slides during transport. As the paper is pulled over these surfaces the friction of the paper across these surfaces produces tension in the print media. In one embodiment, this device allows an adjustment of the positional relationship between surfaces, to control the angle of wrap and allow adjustment of web tension.

TABLE 1 Roller Listing for FIG. 2 Media Handling Component Type of Component A Lateral constraint (edge guide) SW—S-Wrap Zero constraint (non-rotating support). Tensioning. B Angular constraint (in-feed drive roller) C Zero constraint (Castered and Gimbaled Roller) D* Angular constraint with hinge (Gimbaled Roller) E Angular constraint with hinge (Gimbaled Roller) F Angular constraint (Fixed Roller) G Zero constraint (Castered and Gimbaled Roller) H Angular constraint with hinge (Gimbaled Roller) TB(TURNOVER) See FIG. 3 I Zero constraint (Castered and Gimbaled Roller) J* Angular constraint with hinge (Gimbaled Roller) K Angular constraint with hinge (Gimbaled Roller) L Angular constraint (Fixed Roller) M Zero constraint (Castered and Gimbaled Roller) N Angular constraint (out-feed drive roller) O Zero constraint (Castered and Gimbaled Roller) P Angular constraint with hinge (Gimbaled Roller) Note: Asterisk (*) indicates locations of load cells.

The top view of FIG. 3 shows the arrangement and constraint pattern, respectively, for turnover mechanism (TB) 30, shown as part of second module 40 from FIG. 2. Turnover mechanism TB can optionally be configured as a separate module, with its web media handling compatible with that of second module 40. The position of turnover mechanism TB is appropriately between print zones 54 for opposite sides of the media. Here, a fixed, non-pivoting, drive roller 32 of this device provides the single angular constraint. Lateral constraint is provided by the position of the moving web upstream of stationary turn bar 34, from the left in FIG. 3. Stationary turn-bars 34 and 36, respectively upstream and downstream of drive roller 32, are both positioned at diagonals, approximately 45° angles relative to media motion over input and output paths and impart no lateral or angular constraint on the web as it slides over them. The use of a driven roller in the turnover mechanism, which can be driven independently of drive rollers B and N, allows the tension in the web to be separately maintained both upstream and downstream of the turnover mechanism. Although not shown in FIG. 3, a nip roller can be used in conjunction with the driven roller to prevent the web from slipping relative to the driven roller.

The side view of FIG. 4 shows the position of turnover mechanism TB 30 within the support structure of module 40. Fixed drive roller 32 lies behind turn bars 34 and 36 in the arrangement shown. It can be appreciated that this makes it difficult to access drive mechanism components for turnover mechanism 30 and complicates the operator task of feeding the leading edge of the web media over and around rollers and surfaces of turnover mechanism 30.

The enlarged perspective view of FIG. 5 shows an unobstructed view of the roller and turn bar arrangement of turnover mechanism 30 components. The web media feeds from the left and exits downstream to the right. Directions D1-D4 are shown for reference to more clearly describe web travel relative to roller 32 and turn bars 34 and 36 in the following sequence. The web media, initially traveling in direction D1, wraps over the first turn bar 34 and then travels in direction D2 in order to feed toward fixed roller 32. The web then wraps over roller 32 and passes between the roller 32 and nip wheels (not shown in FIG. 5). The web then heads back in direction D3, opposite direction D2, toward the second turn bar 36. Turn bar 36 redirects the web media into direction D4.

Referring to the perspective views of FIGS. 6 and 7 and top view of FIG. 8, an improved arrangement of turnover mechanism 30 according to an embodiment of the present invention uses a set of guides 100, 102, and 104 in order to help alleviate the difficulty of feeding the leading edge of the web media through turnover mechanism 30. First guide 100 is positioned between the first turn bar 34 and drive roller 32 in order to guide the leading edge toward roller 32 in direction D2, as was described with reference to FIG. 5. Second guide 102 is positioned between roller 32 and the second turn bar 36. Second guide 102 helps to guide the leading edge of the web media coming out from roller 32 in direction D3 (FIG. 5) toward turn bar 36. Third guide 104 is positioned to guide the leading edge of the media around turn bar 36 and then out of the turnover mechanism 30 in direction D4 (FIG. 5). FIG. 8 also shows the position of a motor 130 that drives roller 32 rotation as part of a media drive module 140. Motor 130 can be remotely actuable and can have a jog capability to assist the operator in initial media edge guidance and feeding, as described subsequently.

Still referring to FIGS. 6-8, media guides 100 and 102 have substantially flat portions that extend between the fixed roller 32 and corresponding turn bars 34 and 36 and guide the web media along a straight path between the roller and its turn bars. Media guide 104 also has a substantially flat portion that extends away from turn bar 36. In addition, an edge portion of any or all guides 100, 102, and 104 may also provide curvature in order to help guide the leading edge around the corresponding roller or fixed turn bar surface. Guide 100, for example, can have a curved portion 118 to direct the leading edge of the web media around turn bar 34, as shown in FIG. 6. In another example, guide 104 can have a curved portion 108 to direct the leading edge of the web media around the second turn bar 36, as shown in FIG. 6. In the embodiment shown, curved portion 118 has approximately a 55 degree wrap about turn bar 34. In the embodiment shown, this is less wrap than the curved portion 108 of the third guide 104 provides about second turn bar 36.

It should be noted that the wrap angle for any individual guide can be varied to provide an advantageous media edge feed arrangement, based on the design of the turnover mechanism and on characteristics of the intended print media. The amount of wrap provided by any of guides 100, 102, and 104 may vary in other ways. For example, the angular extent of the wrap could vary across the width of the media path for any of the guides, so that a greater or lesser amount of wrap is provided toward one edge of the media path or along the center, for example.

Referring to the side view of FIG. 9, media traveling toward fixed, non-pivoting drive roller 32, on top of guide 100 and in direction D2, is directed along the surface of end portion 106 in order to help direct the leading edge of the media around fixed roller 32. FIGS. 8 and 9 also show a fourth guide 110 that provides a curved surface about roller 32 and is thus positioned to direct the leading edge of the web of media around roller 32 and into nip 112.

Once the leading edge of the web has passed through the nip, the drive roller is turned on at low speed to drive the web forward. An edge portion 122 of fourth guide 110 extends onto second guide 102, extending the contact surface for feeding the leading edge onto the contact surface of guide 102. Media traveling away from roller 32, onto guide 102 and in direction D3, is directed by a lower guide surface 107 back toward guide 102, thereby preventing the leading edge of the web media from wrapping around drive roller 32. Accordingly, in some embodiments of the invention, second media guide 102, extending between fixed roller 32 and turn bar 36, can have a first guide portion (either 107 or 102) located on a first side of the web media and a second guide portion (the other of 107 or 102) for the second side of the media that helps to reduce or even prevent the media leading edge from wrapping around turn bar 36. In the same way as first guide 100 with end portion 106 and fourth guide 110 guided the leading edge of the web around roller 32, second guide 102 and the curved portion 108 of guide 104 direct the leading edge of the web around the second turnbar 36.

Still referring to FIG. 9, fixed roller 32 is a driven roller provided with a nip roller 114 in the embodiment shown. The nip roller can be moved by an actuator 120 between two positions, so that in a first position (as shown in FIG. 9), a force is applied to roller 32 at a nip 112 and in a second position, nip roller 114 is backed away from nip 112 and no force is applied at nip 112. Movement of the nip roller to the second position aids in removal of web portions from around the drive roller in the event of a web break. Actuator 120 is remotely actuable in one embodiment.

FIG. 10 shows fourth guide 110 of FIGS. 8 and 9 from a rear view according to one embodiment. Cutouts or windows 124 in the guide allow guide 110 to fit in place near drive roller 32 without interfering with nip roller 114. Other types of opening could alternately be used. In the embodiment of nip roller 114 shown, the roller is not continuous, but is instead segmented, with a number of sections shown as wheels 126. Each segment is independently rotatable in one embodiment. Segments can alternately be castered and gimbaled to minimize constraint imposed on the moving web media.

It is instructive to note that guides 100, 102, 104, and 110 are provided for feeding the leading edge of the web media during loading by the operator. Once the media leading edge has been fed through turnover mechanism 30, these guides typically do not contact the web media. Thus, during printing, guides 100, 102, 104, and 110 do not provide any constraints to the web media such as edge constraint, for example, and are compatible with a kinematic or exact-constraint web transport path, such as that described in commonly-assigned copending U.S. patent application Ser. No. 12/627,032 filed Nov. 30, 2009 entitled “MODULAR MEDIA TRANSPORT SYSTEM”, by DeCook et al. and commonly-assigned copending U.S. patent application Ser. No. 12/627,018 filed Nov. 30, 2009 entitled “MEDIA TRANSPORT SYSTEM FOR NON-CONTACTING PRINTING”, by Muir et al., both incorporated herein by reference.

Guides 100, 102, 104, and 110 are provided for the leading edge only and need not extend to cover the full width of the web media. This allows guides 100, 102, 104, and 110 to be used with a printing apparatus that accepts web media of various widths. Guides 100, 102, 104, and 110 can be formed from any suitable material, including metal, plastic, or various sheet materials, for example. Guides can be perforated or otherwise featured to reduce weight, increase rigidity, or to aid in their guidance function.

In one embodiment, guides 100, 102, 104, and 110 are used by the operator in conjunction with a partially automated media feed apparatus that allows the operator to feed and direct the leading edge into proper position with each turn bar or roller mechanism and use a mechanized sequence to jog the media along the path until it is fed through turnover mechanism 30.

In operation, with reference to FIG. 8, the operator follows a sequence of steps for feeding the web media through turnover mechanism 30 by steps of:

-   -   (i) threading the leading edge of the web media around first         turn bar 34 with the aid of curved portion 118 and along first         guide 100 toward fixed roller 32 and associated nip 112 (FIG.         9);     -   (ii) entering a jog command, such as by depressing a switch,         causing roller 32 to rotate momentarily at a slow speed;     -   (iii) pushing the leading edge along the top surface of first         guide 100 to urge the leading edge around drive roller 32 guided         by fourth guide 110 until the web is captured between nip roller         114 and drive roller 32;     -   (iv) continuing the jog command and observing drive roller 32         action that feeds the leading edge onto the top surface of         second guide 102, with the web moving back toward the operator;     -   (v) threading the leading edge of the web media around second         turn bar 36 guided by the curved portion 108 of third guide 104;         and     -   (vi) terminating the jog command when the leading edge is fed         out from second turn bar 36 along the third guide 104.

It can be appreciated that steps (i)-(vi) given above are illustrative and can be modified in a number of ways and augmented with any of a number of automated operations. An optional operator switch or other control for enabling jog operation can be provided with a separate device or provided as part of turnover mechanism 30. Additional rollers or other components can be provided to support media feed through drive roller 32.

The turnover mechanism 30 described herein can be used with a modular printing apparatus arrangement as described earlier with respect to FIGS. 1 and 2 or with some other printing apparatus configuration that is not modular. Slack loops are not required between or within modules or other parts of the system. Slack loops can be appropriate where a continuous web is initially fed from a supply roll or as it is re-wound onto a take-up roll, as was described with reference to the printing apparatus of FIG. 1.

FIGS. 9, 11, and 12 show various side views of media drive module 140 according to one embodiment of the present invention. Fourth guide 110 has at least a first position, adjacent to roller 32 as shown in FIG. 11, used for guiding the lead edge of the web of media into the nip between the nip roller 114 or nip wheels 124 and the drive roller 32. FIG. 12 shows guide 110 in a second position, removed from roller 32. This second position is used to provide access to a portion of roller 32. With the guide in the second position and the nip roller 114 moved to the second position by actuator 120, media fragments can be readily removed from around the drive roller in the event of a media break or media jam at the drive roller. A hinge 142 or other mechanism enables mechanical movement of guide 110 between first and second positions. Alternately various other types of mechanisms could be used to allow movement between first and second positions, using techniques well known in the mechanical arts. An optional latch mechanism (not shown) is used in one embodiment to temporarily hold guide 110 in its second position during leading edge feed activity. Latching mechanisms can include magnets, springs, pins, detents, or other mechanical devices that help to temporarily hold guide 110 in place. Guide 110 can be self-closing, using gravity, spring-loading, or magnetic attraction, for example.

As shown in FIG. 11, guide 110 has a contact surface 144; guide 102 has a contact surface 146. Contact surface 144 can extend onto contact surface 146. Alternately, contact surfaces 144 and 146 can be offset relative to each other such that guide 110 ensures that the media is directed to the proper side of the downstream guide 102.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.

PARTS LIST

-   -   10. Printing system     -   12. Media supply roll     -   16. Digital printhead     -   18. Media take-up roll     -   20. Module     -   22. Cross-track positioning mechanism     -   24. Tensioning mechanism     -   26. Constraint structure     -   30. Turnover mechanism     -   32. Drive roller     -   34, 36. Turn bar     -   40. Module     -   48. Support structure     -   52. Slack loop     -   54. Print zone     -   90. Control logic processor     -   100, 102, 104. Guide     -   106. End portion     -   107. Guide surface     -   108. Curved portion     -   110. Guide     -   112. Nip     -   114. Roller     -   118. Curved portion     -   120. Actuator     -   122. Edge portion     -   124. Opening     -   126. Wheel     -   130. Motor     -   140. Media drive module     -   142. Hinge     -   144, 146. Contact surface     -   A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P. Rollers     -   D1, D2, D3, D4. Direction

SW. S-wrap

-   -   TB. Turnover mechanism 

1. A media turnover mechanism comprising: a roller; a first turn bar positioned upstream relative to the roller, the first turn bar being positioned at an angle relative to a direction of media motion; a second turn bar positioned downstream relative to the roller, the second turn bar being positioned at an angle relative to a direction of media motion; a first guide positioned between the first turn bar and the roller to direct a leading edge of a web of media toward the roller; a second guide positioned between the roller and the second turn bar to direct the leading edge of the web of media toward the second turn bar; and a third guide positioned to direct the leading edge of the web of media around the second turn bar.
 2. The mechanism of claim 1 wherein the second guide includes a first guide portion located on a first side of the media and a second guide portion located on a second side of the media.
 3. The mechanism of claim 1, wherein a portion of the first guide is positioned to direct the leading edge of the web of media around the first turn bar.
 4. The mechanism of claim 1, further comprising: a fourth guide positioned to direct the leading edge of the web of media around the roller.
 5. The mechanism of claim 4, wherein the fourth guide is hinged such that the fourth guide includes a first position adjacent to the roller to direct the leading edge of the web of media and a second position removed from the roller that provides access to at least a portion of the roller.
 6. The mechanism of claim 5, wherein the roller is a driven roller.
 7. The mechanism of claim 6, the roller being a first roller, further comprising: a second roller including a first position in which the second roller applies a force to the driven roller and a second position removed from the driven roller.
 8. The mechanism of claim 4, wherein a portion of the fourth guide extends to the second guide that is located downstream relative to the roller.
 9. The mechanism of claim 1, wherein a wrap of the third guide relative to the second turn bar is greater than a wrap of the first guide relative to the first turn bar.
 10. The mechanism of claim 1, wherein a wrap of the third guide relative to the second turn bar varies along a length of the second turn bar. 